In electrical and electronic systems, the noise generated by amplification of a signal reduces the signal to noise ratio and creates a limitation in the creation of good-quality high-power RF signals.
Elimination of the noise generated by amplification of a signal is valuable in many applications, including communications, military applications and measurement systems.
Prior known amplifier circuits have used feedforward superposition to isolate amplifier generated noise and subsequently cancel the amplifier generated noise in the output signal. Such amplifier circuits are subject to drift due to time, temperature and power variations. Amplifier characteristics also vary for different signal frequencies within the amplifier bandwidth. Many prior known feedforward amplifier circuits were optimized during initial setup and did not provide automatic compensation for drift and frequency variation.
Prior known amplifier circuits have used feedback modulation of the input signal to attempt to suppress amplifier generated noise. Attempts to combine feedforward superposition and modulation have generally resulted in rather complex amplifier circuits. U.S. Pat. No. 5,760,646 to Belcher et al. discloses an amplifier circuit that uses complex work functions to attempt to predistort the input signal to an amplifier. U.S. Pat. No. 6,087,898 to Baskin discloses a complex amplifier circuit that uses a pilot tone and two feedforward loops to attempt to suppress amplifier generated noise.
A relatively simple, cost effective amplifier circuit that provides automatic compensation for drift due to time, temperature, and power variations, and to frequency variation is desirable.